Hardened gelatin compositions and a method of hardening same

ABSTRACT

A hardened gelatin composition and a method of hardening said gelatin composition wherein the gelatin is hardened by the addition of a pyrrolidonyl polyacrolein-bisulfite addition compound.

United States Patent [72] Inventors Nathan D. Field Allentown; David I. Randall, Easton, Pa.; Jimmie D. Fitzpatrick, Lafayette, La. [21] Appl. No. 799,089 [22] Filed Feb. 13, 1969 [45] Patented Oct. 26, 1971 [73] Assignee GAF Corporation New York, N.Y.

[54] HARDENED GELATIN COMPOSITIONS AND A METHOD OF HARDENING SAME [50] Field of Search 96/111; l06/l25;260/117,72

[56] References Cited UNITED STATES PATENTS 3,226,234 12/1965 Himmelmann et al 96/111 3,396,029 8/1968 Himmelmann et al 96/111 Primary Examiner-Norman G. Torchin Assistant Examiner-Richard E. Fichter Attorneys-Samson B. Leavitt and Walter C. Kehm ABSTRACT: A hardened gelatin composition and a method of hardening said gelatin composition wherein the gelatin is hardened by the addition of a pyrrolidonyl polyacroleinbisulfite addition compound.

HARDENED GELATIN COMPOSITIONS AND A METHOD OF HARDENING SAME The instant invention is directed to the hardening of gelatin and the gelatin compositions which result therefrom, and in particular the instant invention relates to the use of pyrrolidonyl polyacrolein-bisulfite addition compounds as hardening agents in gelatin layers.

It is extremely important for photographic products to have layers which are more resistant to water and aqueous processing solutions, swell to a lesser extent and have a higher layer melting point than pure gelatin layers. This is achieved by treating the gelatin with various substances which are able to react with the gelatin by cross-linking of the protein chains. This process is designated as hardening. Such hardening should not, however, result in the gelatin losing its water permeablity. With the known hardening agents hardening is generally started after drying of the layer and reaches its maximum after a few weeks. A large number of compounds are known which are certainly effective, but they harden in a manner which is unpredictable and cannot therefore be accurately controlled, so that when the photographic materials are stored, the sensitometric properties thereof are changed.

Many types of compounds have been proposed as hardening agents including metal salts, such as chromium, aluminum and zirconium salts; aldehydes and halogenous aldehyde compounds, such as formaldehyde, dialdehydes and mucochloric acid; 1,2- and l,4-diketones, such as cyclohexane-l,2-dione; quinones, chlorides of dibasic organic acids; dianhydrides of tetracarboxylic acids; compounds with several reactive vinyl groups, such as vinyl sulphones, acrylamides; compounds with at least-2 heterocyclic rings which can easily be split off, such as ethylene oxide and ethylene imine; polyfunctional methane-sulphonic acid esters. These hardening agents are generally compounds of low molecular weight.

Some of these compounds are photographically active and consequently cannot be considered for certain photographic silver halide emulsions. Other known compounds having a hardening action are not suitable for other reasons. For example, metal salts increase the brittleness of the layers, dialdehydes color the layers, anhydrides and acid chlorides have the disadvantage of changing the pH value of the emulsion during the initial hardening. All compounds of low molecular weight have the disadvantage of not limiting their hardening to specific layers of photographic multilayer materials since they are diffusible and can penetrate through all layers. In addition hardening with the said hardening agents is not controllable since the hardening starts after drying and increases during storage. This effect is designated as after-hardening. With some photographic paper emulsions, this effect is extremely disturbing, since the tone of the developed silver image of such papers is changed with increasing period of storage prior to exposure. For photographic papers, especially brown toning papers, it is consequently important to find a hardener which has little effect when incorporated in the layer, even when stored for relatively long periods before processing, but produces a substantial increase in the melting point of the layer during development. The developed papers can then be stored for relatively long periods with only slight effect on the image tone.

in addition to the hardeners of low molecular weight referred to above, others are known which are of high molecular weight. Thus, polyaldehydes, such as the periodic acid oxidation products of starch, have been described as hardeners. However, they have the disadvantage of possessing only a low hardening equivalent, since even in the most favorable case only two aldehyde groups are present to each hexose unit. The maleic acid semiesters of alcohols of high molecular weight, such as polyvinyl alcohol, have similar disadvantages.

As noted above, many of the hardeners exhibit numerous unwanted photographic effects of one kind or another. For instance some aldehyde type hardeners have shown a tendency to cause an increase in fogging of the emulsion. Other types of hardeners have a tendency to cause loss of speed of the emulsion upon storage. It is desirable that hardeners for gelatin particularly when used in photographic emulsions will not adversely affect the photographic characteristics of the emulsion. This also extends to photographic gelatin layers which often contact the photographic emulsion layers in use.

Furthermore, previously employed gelatin hardeners especially those of the chrome alum type have a tendency to lose most of their hardening effects at the higher pHs of the photographic developing and toning solutions used for the processing of photographic emulsions.

Therefore, it is an object of the instant invention to provide hardeners for gelatin which do not exhibit detrimental photographic effects.

Another object of the instant invention is to provide a material suitable for hardening of gelatin, which material is effective at the high pl-ls normally employed in photographic processing.

Yet another object of the instant invention is to provide a a hardening agent for a gelatin which has a delayed action.

Still another object of the instant invention is to provide a hardener which does not effect adversely the photographic effeet as the pH of the emulsion is varied.

These and other objects of the instant invention will become more evident from the following more detailed description thereof.

We have found that the addition compounds which result from the reaction of bisulfite with pyrrolidonyl polyacrolein are useful in the instant invention. The pyrrolidonyl polyacrolein used in the preparation of the hardening agents of interest for the instant invention are in general prepared by the reaction of polyacrolein with 2 pyrrolidone as disclosed in our copending application, Ser. No. 799,072 filed 13 Feb. l969. The products are specifically named Z-pyrrolidonyl-l polyacrolein and will be referred to herein as pyrrolidonyl polyacrolein.

We have found that normally insoluble polyacrolein may be made soluble by reacting said polyacrolein with pyrrolidone. In general the useful polyacrolein compounds include those which are prepared from a, B-ethylenically unsaturated aldehydes, i.e., those compounds which have an ethylenic group in the 01,6 position relative to the aldehyde group, such as, for example, acrolein, aand B-substituted acroleins such as aethylacrolein, a-isobutylacrolein, a-chloroacrolein, fi-phenylacrolein, a-decylacrolein, a-cyclohexylacrolein, etc. The preferred aldehydes include alpha, beta-monoethylenically unsaturated monoaldehydes containing from three to 12 carbon atoms, and especially the alpha and beta-substituted acroleins wherein the substituent on the alpha and/or beta positions is an alkyl, cycloalkyl or aryl group containing no more than eight carbon atoms. 2-alkenals containing up to eight carbon atoms come under special consideration. These aldehydes may in general be prepared by spontaneous polymerication of acrolein which on standing results in a solid, nonfusible and insoluble product which has been designated as disacryl (Redtenbacher, Liebigs Ann. Chem. 47 I843) p. 113. Furthermore, as stated above, acrolein polymerizes under the influence of free radical forming catalysts to produce insoluble polymers which are insoluble in known organic solvents. Suitable catalysts which may be employed include, among others, the peroxides, such as benzoyl peroxide, hydrogen peroxide, potassium persulfate, alkali perborates, diacetyl peroxide, tertiary butyl hydroperoxide, tertiary amyl hydroperoxide, ditertiary butyl peroxide, ditertiary hexyl peroxide, acetylbenzoyl peroxide, cumene hydroperoxide, tetralin hydroperoxide, phenylcyclohexane hydroperoxide, tertiary-butylisopropyl benzene hydroperoxide, tertiary butyl peracetate, tertiary butyl perbenzoate, ditertiary butyl phthalate, ditertiary butyl peradipate, tertiary butyl et-carbonate and the like, and azo catalysts, such as organic compounds containing an N=N group as alpha, alpha'-azodiisobutyronitril, alpha, alpha-diisobutyrate, alpha,alpha'- azobis(alpha,gamrnadimethylvaleronitrile), alpha,alphaazodiisobutyramide, alpha,alpha-azobis(alpha-cyclopropylpropionitril), alpha,alpha'-(alpha-methylbetaphenylpropionitril), alpha-(carbamylazoisobutyronitril), alpha-azobis(alpha-cyclohexylpropionitril), 1 azodicyclohexanecarbonitrile, diazoaminobenzene, 1,1 azobis(l-phenylethane) and the like, and various aldoximes, ketoximes, azines and the like.

The polymers of the above-described unsaturated aldehydes to be employed in preparing the new derivatives of the present invention are those obtained by addition polymerization through the double bond and those having a high molecular weight, i.e., those having a molecular weight above 50,000 and preferably between 100,000 and 2,000,000, said molecular weights being determined by the light scattering technique. The molecular weight range may also be indicated by intrinsic viscosity values as these are usually more easily determined. Preferred polymers are those having intrinsic viscosities (as determined on the solubilized form of the polymer) of at least 0.9 dl./g. and preferably between 0.9 dl./g. and 5.0 d1./g. These values are determined by the conventional technique of polyelectrolyte viscosity measurements at 25 C.

We have found that when the above-noted high molecular weight polyacroleins are placed in contact with pyrrolidone, they dissolve quite readily even up to about percent by weight. This solubility is attributed to the formation of a new product, herein referred to as pyrrolidonyl polyacrolein. Furthermore, this solution appears to occur without appreciable reduction in the molecular weight of the polyacrolein. Also the aldehyde function is still present, as is evidenced by its ready reaction with aqueous S0 (sulfurous acid) or sodium bisulfite to form new bisulfite addition products as claimed in our copending application, Ser. No. 799,108 filed 13 Feb. 1969.

The pyrrolidonyl polyacrolein product of the instant invention is stable, as evidenced by the fact that pyrrolidone is not removed by treatment with hot water, dilute acid nor by reaction with $0 or aqueous metal bisulfite solutions. The reaction with metal bisulfites is quite surprising since the entire polymer dissolves in water as the bisulfite addition product without the loss of a pyrrolidone moiety.

The pyrrolidonyl polyacrolein then may be reacted with sulfur dioxide or a bisulfite and the like to form the useful addition compounds employed herein. The preparation of the bisulfite addition compound of pyrrolidonyl polyacrolein is more fully described in our copending application, ser. No. 799,108.

The above-described pyrrolidonyl polyacrolein is reacted with an aqueous solution of a bisulfite compound or S0 The suitable bisulfite compounds which may be employed in accordance with the process of this invention can be represented by the generic formula M(HSO )m, wherein M designates a metal atom and m is the valence of M. Suitable metal bisulfrtcs include, for example, the bisulfites of metals of Groups 1A, 1 IA, and l 1 1A of the Periodic Table as set forth in the Handbook af Chemistry and Physics, 38th ed., pp. 394-395, such as sodium bisulfite, potassium bisulfite, calcium bisulfite, magnesium bisulfite, aluminum bisulfite, etc. Of these, the alkali metal (Group 1A) bisulfites, and especially sodium bisulfite and potassium bisulfite, are preferred for use in the process of this invention. Similarly, ammonium bisulfite can also be employed. The suspension of the bisulfite can be effected by the incorporation in the diluent of the metal bisulfite as such, or as the corresponding pyrosulfite (meta-bisulfite) which, upon incorporation, forms the metal bisulfite. In addition one may, as noted above, also use an aqueous solution of sulfur dioxide.

The pyrrolidonyl polyacrolein bisulfite addition product may be prepared by process steps which include bringing into reactive admixture a suspension of pyrrolidonyl polyacrolein and a metal bisulfite of the formula M(HSO;,)m, wherein M is a metal atom and m is the valance or ionic charge of M, in a single-phase liquid diluent consisting essentially of a solution composed of water. The reaction can be illustrated by the equation:

alpha,

oa -0H mason... Lem-cra (m-l oHoHJ g $03-- in wherein M and m are as defined above. It is to be noted that when M designates a divalent or polyvalent metal, the metal is connected to two or more polymerized acrolein units in the resulting product, depending upon its valence. It is also to be noted that polyacrolein, as is well known to the art, is a complex structure which, it is believed, contains polymerized acrolein units possessing free aldehyde groups, as indicated above, as well as units in which the aldehyde groups are masked in the form of aldehyde hydrate and acetal linkages. See, for instance, the article by Schulz, R. C., Polymerization of Acrolein, in Kinetics and Mechanism of Polymerization, G. E. Ham, Ed., M. Dekker, N.Y., Vol. 1, Pt. 1 Vinyl Polymerization, l967, p. 410 or US. Pat. No. 3,235,524 issued Feb. 15, 1966 to Kern, Schweitzer Schulz. Under any circumstance, the polymer has been found to react with bisulfite as herein described to form the adducts contemplated by this invention.

In general, we have found that when one adds a solution of pyrrolidonyl polyacrolein-bisulfite to a photographic emulsion such as a photographic gelatin silver halide emulsion, one may obtain hardening thereof. Furthermore, we have found that with the use of pyrrolidonyl polyacrolein-bisulfite one may obtain a product in which very little hardening takes place during storage, which product, once it is treated with alkaline developing and toning solutions, produces a very good and strongly pronounced hardening action.

When one adds the pyrrolidonyl polyacrolein-bisulfite addition product disclosed herein to an aqueous gelatin solution which is used in the preparation of a surface layer for the gelatin silver halide emulsion layer, one obtains a photographic product in which very little hardening will take place during storage prior to processing. However, when the photographic product so produced is treated during a development process at relatively high pl-l s of from about 7 to 12, one obtains a very good and strongly pronounced hardening adduct. With such a product, i.e., a gelatin containing photographic product to which has been added pyrrolidonyl polyacroleinbisulfite, offers several advantages over similar products previously known since such a product which includes pyrrolidonyl polyacroleinbisulfite promotes hardening at higher phs whereas the previously employed chrome alum type hardeners lost most of their hardening action at these pHs which are commonly employed in photographic processes.

The water-soluble pyrrolidonyl polyacrolein-bisulfite addition products are utilized in accordance with the present invention in the hardening of a gelatin composition, e.g., a photographic gelatin silver halide emulsion layer or gelatin surface or intermediate layer by incorporating the addition product coated in such gelatin layer or gelatin silver halide emulsion layer either directly prior to coating or by immersion of the gelatin-containing composition into a solution of the pyrrolidonyl polyacrolein-bisulfite. When added tothe gelatin or gelatin silver halide emulsion layers, the addition products are generally employed in an amount effective to produce the desired hardening of the gelatin. Generally such an amount varies from about 1 percent to 10 percent by weight based on the amount of gelatin present. Slightly lesser or greater amounts are also useful for specific particular purposes. When an aqueous solution of-the condensation product is employed to provide the necessary hardening for a gelatin emulsion layer, generally the amount of hardener present in such aqueous solution is such that the desired hardening effect may be obtained. Here again, solutions containing from about 1 percent to about 10 percent by weight of the addition products have been found applicable for use. Once again, when one desires to use the addition products for a particular purpose, the amounts may be varied according to said purpose.

The present invention is applicable to the hardening of any and all conventional gelatin silver halide photographic emulsion layers. For example, the process and composition of the instant invention may be employed in connection with the gelatino silver bromide, gelatino silver iodide, gelatino silver chloride, gelatino silver iodide-silver bromide, gelatino silver bromide-silver chloi icl e etc. Thus, all such conventional silver halide photographic emulsions containing gelatin can be hardened in accordance with the process and composition of the present invention.

In addition, the composition and process of the instant invention may be employed in connection with all conventional developing compositions which are generally applicable for the development of gelatin silver halide type emulsion layers.

It had been previously proposed to use polyacroleinbisulfite as a hardener for photographic gelatin layers and gelatin silver halide emulsion layers. These compounds harden satisfactorily under alkaline conditions but suffer from the disadvantage that they must be added to these gelatin layers under very narrow pH conditions which must not vary by more than 0.1. Thus, the polyacrolein-bisulfites of the prior art serve satisfactorily at a pH of between 5.2 and 5.3 but cause considerable fog once the pH is raised to a value of 5.4 to 5.6. On the other hand, the pyrrolidonyl polyacroleinbisulfites of the instant invention can be used without any deleterious effects within a pH range offrom 5.0 to 6.0.

The hardening agents of this invention do not need to be used by themselves but can be combined with other inorganic or organic hardening agents. Thus, the pyrrolidonyl polyacrolein-bisulfite can be used in combination with inorganic hardening agents such as alum or potassium chrome alum or with organic hardening agents such as formaldehyde, glyoxal or mucochloric acid. This combination of hardening agents provides a preliminary hardening prior to the alkaline processing steps while resulting in a sustained and permanent hardening by the action of the pyrrolidonyl polyacroleinbisulfite during the alkaline processing.

The present invention will now be described by reference to the following specific examples. Such examples are presented for purposes ofillustration only, and the present invention is in no way to be deemed as limited thereto.

EXAMPLE 1 Twenty five g. of polyacrolein prepared by redox polymerization of acrolein in an aqueous medium with a redox system composed of potassium persulfate and silver nitrate was added to 475 g. of 2-pyrrolidone and heated to 80C. with stirring for 4 hours. The resulting viscous yellow solution was filtered through a sintered glass filter. The solution was added to 3 liters of acetone to yield a pale yellow powder which upon drying at room temperature weighed 26.1 g. and analyzed as follows: C, 59.66%; H, 7.54%; and N,4.54%.

EXAMPLE la In the preparation of the polyacrolein, there was charged to a 21 g. multinecked spherical flask with stirrer, condenser, thermometer, temperature controller and nitrogen purge, 1354.4 grams of water and 175.1 grams of freshly distilled acrolein. This was heated to 45 C. with nitrogen purging. Then, with stirring, 25.0 grams of potassium persulfate was added, the nitrogen purge continued, the stirring continued and the temperature maintained at 45 C. for 2 days. During this time the batch became white and thick with precipitated polyacrolein. The slurry was filtered, washed well on the filter with water and dried in a vacuum oven. Yield was 61.2 grams white powder. 1R bands at 2.9, 3.42, 5.8, 6.12, 6.86, 7.17, 7.35, 7.52, 9.75, 12.05 microns.

EXAMPLE 2 90 g. of polyacrolein prepared by the method of example 1 was added to 450 g. of 2-pyrrolidone and heated to 80 C. with stirring for 4 hours. The procedure of example 1 was followed and the results obtained were similar thereto. The precipitated pyrrolidonyl polyacrolein was found to be soluble in N- methyl-2-pyrrolidone, pyrrolidone, dimethyl formamide and hexamethyl phosphoramide. Analysis of the product resulted in the conclusion that a minimum ratio of about 1 pyrrolidone unit per 4 acrolein units were present in the pyrrolidonyl polyacrolein product.

EXAMPLE 2a In preparation of the pyrrolidonyl polyacrolein, 21 g. polyacrolein from example la and 200 ml. benzene were mixed in a reflux flask and 28 g. 2-pyrrolidone were added. The batch was refluxed for 4 hours, the solid filtered off, washed with additional benzene by reslurrying and refiltering, and then dried. This material was found to contain 3.61 percent nitrogen. This corresponds to l pyrrolidone unit reacted per 5.28 acrolein units.

EXAMPLE 3 26.1 g. of pyrrolidonyl polyacrolein prepared by the method of example 2 was stirred at room temperature with 225 g. of an 8 percent aqueous solution of sulfur dioxide for a period of 4 hours. After this time, complete solution had been effected. The resulting pale yellow solution was filtered and nitrogen was bubbled through said solution for approximately 4 hours.

EXAMPLE 3a The product of example 2a was treated by the procedure of example 3. The resultant solution of the product was adjusted to pH of 5.5. The thus obtained product was incorporated in gelatin and tested by usual procedures. The product was more stable than polyacrolein bisulfite at pHs above 5, as shown by complete lack of photographic fogging.

EXAMPLE 4 One gram of the compound prepared in accordance with example 3a was added to l kilogram of a silver bromochloride emulsion of the type which is used for the manufacture of an enlarging, portrait paper. The bromidezchloride ratio was 70:30. The emulsion contained 7 percent by weight of gelatin and an amount of silver halide corresponding to 18 grams of metallic silver. The pH of this emulsion was adjusted to 5.3 and the emulsion was then coated by means of an 8-inch loop coated onto a suitable base. Two comparison emulsions were coated, one without a hardener and the other hardened with polyacrolein-bisulfite. The materials were developed for 1% minutes at a temperature of 68 F. in a developer solution having the following combination:

Calgon (sodium hexameluphosphate) 1.0 g. Potassium Metabisulfite 3.5 g. Metol (p-methylaminophenol sulfate) 0.5 g. Phenidone (l-phenyl-3-pyrazolidone) 0.1 g. Sodium Sulfate 12.0 g. Hydroquinone 3.5 g. Sodium Carbonate (monohydrate) 24. g. Potassium Bromide 0.3 g. Benzotriazole 0.03 Water to make 1 liter Unhardened Polyacrolein- Pyrrolidonyl Poly Material Bisulfite Acrolein-Bisulfite Developer 35 120 Toning 35 I45 136 Bath The photographic properties of all coatings were essentially TABLE 2 the same and included a fog value of 0.09, a Log E speed of i 8.7 and a maximum density of 1.47.

The above-described experiments were repeated but the pH cum! "Pmcessed j of the three liquid emulsions was raised from 5.3 to 5.7. The 5 Fresh zo'day photographic properties of the pyrrolidonyl polyacroleinbisulfite remained the same, but the fog of the sample contain- 2 54 52 s3 52 153 155 mg the polyacrolem-bisulfite increased from 0.09 to 0.21 and 3 62 164 the Log E speed dropped from 8.70 to 8.50. The changes became even more pronounced when the hardened materials 1 r were developed for 8 minutes in a commercially available wh i l i d i GAF Vividol developer. In this instance, the fog of the 1. Th thod f hardening hotographic gelatin which polyacrolein-bisulfite hardened material increased from 0.09 comprises incorporating th i in gelatin hardening amounts to 0.31. the gelatin hardening agent comprising the bisulfite adduct 0 It will be evident from the foregoing description that the 15 -py y Polyacrolein, Said Polyacrolein moiety pyrrolidonyl polyacrolein-bisulfite hardened silver halide g a molecular Weight of at east 50,000 emulsion tolerated an increase in the pH of the emulsion from t0 whereas the polyacrolein-bisulfite hardened materi- 2 Thg process of producing a hardening gciatino silver haal suffered from a considerable increase of fog and a decrease lide emul ion layer which comprises adding the gelatin in p hardening agent of claim 1 to a melted gelatino silver halide emulsion and subsequently coating said emulsion on a suitable EXAMPLE 5 base Pyrrolidonyl polyacrolein-bisulfite was used as a hardener in the emulsion layer of example 4 which was then overcoated 3, A gelatin layer containing as the hardening agent therefor with a 2 percent gelatin surface layer. Processing was similar the elatin hardening agent of claim 1. to the one described in example 4, except that the Vivitoner ig gg gzs by a toner Soluuon having the following 4. A composition of matter comprising an aqueous solution p of gelatin containing in gelatin hardening amounts, the gelatin hardening agent ofclaim 1. Sodium Polysulfide 7.5 g. Potassium Carbonate 2.0 g. Water In make liter 5. The composition of claim 4 wherein the gelatin hardening agent is present in an amount of from about 1 percent to about The results obtained are shown in table 1 The results of a 10 m'b i h fth l i 20-day aging test are shown in table 2. it 1k TABLE 1 pH Melting point, C.

Black and Mg. hardener, Emul- Unnrocwhite Coating Hardening system kgr emulsion sion Surface essed process Toned 1 ,Q, Potassium chrome alum, 0.8 g. per kg.; formaldehyde 37%, 3 70-160 5.6 5. 2 54 132 106 2 Piiigs i u ni %hrome alum, 0.8 g. per kg.; formaldehyde 37%, 3 70-160-800 5. 3 5. 2 53 147 153 ml. per kg.; pyrrolidonyl polyacrolein bisulfite 5%. 3 Potassium chrome alum, 0.8 er kg.; formaldehyde 37%, 3 701601200 5.3 5.2 61 134 157 D ml. per kg.; pyrrolidonyl pofyacrolein blsulfite 5%. 

2. The process of producing a hardening gelatino silver halide emulsion layer which comprises adding the gelatin hardening agent of claim 1 to a melted gelatino silver halide emulsion and subsequently coating said emulsion on a suitable base.
 3. A gelatin layer containing as the hardening agent therefor the gelatin hardening agent of claim
 1. 4. A composition of matter comprising an aqueous solution of gelatin containing in gelatin hardening amounts, the gelatin hardening agent of claim
 1. 5. The composition of claim 4 wherein the gelatin hardening agent is present in an amount of from about 1 percent to about 10 percent by weight of the gelatin. 